We examined the 12-lead ECG recorded within 2 months of death in 50 patients aged 16 to 65 years (mean 48) with peak systolic pressure gradients (PSPG) across the aortic valve ranging from 52 to 180 mm Hg (mean 98) and anatomically normal mitral valves. Measurement of the total 12-lead QRS amplitude, which ranged from 144 mm (10mm=1mV), (mean 257) proved useful for it correlated directly with PSPG across the aortic valve and, when the four LBBB patients were excluded, with the peak LV systolic pressure. The total 12-lead QRS amplitude (mm) was similar in most patients to the LV systolic pressure (mm Hg). Thus, subtraction of the indirect systemic arterial systolic pressure (mm Hg) from the total 12-lead QRS amplitude (mm) provides a reasonable nonivasive prediction of the PSPG across the aortic valve in patients with moderate to severe AS.